Sensors are devices that measure a physical quantity and convert it to a signal that can be measured by an observer or an instrument. Numerous types of sensors exist including sensors for chemical, biological, mechanical, and optical applications, as well as sensors for combinations of these types of applications. A chemical sensor is a device that furnishes the user with information about its environment. It consists of a physical transducer and a chemically selective layer. The universal molecular sensors made in accordance with the present invention are particularly suited for use as chemical sensors or biosensors. Performance of a sensor is measured by the sensor's selectivity, sensibility, and stability. It is difficult to achieve high levels of all three of these functions at the same time because the sensor's sensing process is actually a molecular recognition process. Molecular recognition includes not only chemical (or biological) recognition, as mentioned above with respect to a chemical sensor, but also physical recognition.
The importance of physical recognition has been realized in the field of sensors by utilizing molecular imprinting to make sensors. Molecular imprinting is a known technique for making synthetic hosts which are the man-made mimics of biological receptors or enzymes that possess sites for molecular recognition and catalysis. Molecular imprinting involves creating template-shaped cavities in polymer matrices with the memory of the template molecules used for molecular recognition. This system is based on the “lock and key” model which is the system used by enzymes for substrate recognition. Enzymes have active binding sites with a unique geometric structure which selectively bind to a substrate having a corresponding shape.
In prior art molecular imprinting processes, substrate-selective recognition sites are prepared in a matrix using a casting procedure with a template molecule. Functional monomers attach to, or assemble around, a template molecule and the functional monomers and the template molecule are subsequently linked together by a cross-linking agent to form a molecularly imprinted polymer network. Removal of the template molecule from the molecularly imprinted polymer network creates a structure complementary to the template structure allowing its tight and selective uptake.
Despite the broad use of the above described molecular imprinting technique, there are inherent limitations with this process that decrease its practical suitability for sensors and other applications such as use in bioanalytical assays. For example, one inherent limitation is the inability for polymers to generate molecule size cavities with structure details due to the non-structure orientation around the templates and the macro-scale nature of the prior art molecular imprinting process. It is difficult to use a polymer as a building matrix to make molecule size recognition hosts. Another limitation is that the molecular recognition for sensor application is separated from transduction. For example, in nature, where there are ion channels in membranes, it is hard to distinguish molecular recognition from transduction, the two main components of sensors, as they are integrated and not separable. Other limitations and problems with the prior art molecular imprinting technique described above include heterogeneity in binding affinities, slow mass transfer in and out of the polymer matrix or network, overall low binding affinity, lack of a read-out for complexation, and slow template leaching.
Accordingly, there is a need for sensors and a method for producing sensors that overcomes these limitations and problems. In particular there is a need for sensors with enhanced selectivity, sensibility, and stability that provide molecular recognition cavities with antibody-like ability to bind and discriminate between molecules or other structures, and methods for making the same. The discovery of a nano-tunneling effect in sensors made in accordance with the present invention will open a new view point to current science. The application of a nano-tunneling effect in sensors made in accordance with the present invention can be used to build next generation biosensors and can also be used in other analytical assay applications.